Switching to Hidden Metallic Crystal Phase in Phase-Change Materials by Photoenhanced Metavalent Bonding

Won Jun Yang, Taewoo Ha, Byung Cheol Park, Kwang Sik Jeong, Jae Yeon Park, Dasol Kim, Changwoo Lee, Jaehun Park, Mann Ho Cho

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1 Citation (Scopus)


Metavalent bonding is crucial for the determination of phase transition and improvement of device performance in phase-change materials, which are attracting interest for use in memory devices. Although monitoring dielectric and phononic parameters provides a direct measure of the metavalent bonding, the control of phase-change phenomena and metavalent bonding in the dynamical regime has yet to be demonstrated. This study reports the photoenhanced metavalent bonding and resulting hidden metallic crystalline state of Ti-doped Sb2Te3, a representative phase-change material with ultralong sustainability. Using ultrafast terahertz spectroscopy, Ti0.4Sb2Te3 was discovered to possess ultralong pump-probe dynamics, which is retained over hundreds of picoseconds, unlike the short-lived state of undoped Sb2Te3. Moreover, for Ti0.4Sb2Te3 during the long-lived transmission change, the infrared-active phonon is highly softened, even more than the amount of a thermal phonon shift, indicating the photoenhancement of lattice anharmonicity. Such a long-lived relaxation implies photoinduced transition into a crystalline state of ultrastrong metavalent bonding in Ti0.4Sb2Te3, on the basis of comparisons of the dynamical dielectric constant and temporal phonon shift. Our results show the realization of photoengineering of phase-change materials by tuning electron sharing or transferring.

Original languageEnglish
Pages (from-to)2024-2031
Number of pages8
JournalACS Nano
Issue number2
Publication statusPublished - 2022 Feb 22

Bibliographical note

Funding Information:
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Government of Korea (MSIP) (No. 2018R1A2A1A05023214) and the Ministry of Trade, Industry & Energy (MOTIE) in Korea (Project No. 10080625), and Korea Semiconductor Research Consortium (KSRC) through a project for developing source technologies for future semiconductor devices.

Publisher Copyright:
© 2022 The Authors. Published by American Chemical Society

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)


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